Pulse motor assembly

ABSTRACT

A pulse motor assembly comprising a plurality of synchronous motors connected in tandem. Each of the synchronous motors includes a rotor having pole teeth each tapering towards its free end which is formed as a sharp pointed end. The north and south poles of permanent magnet stator included in the respective synchronous motors are staggered from each other by a distance equivalent to one pole pitch divided by the number of the synchronous motors connected.

United States Patent Inariba [45] Sept. 19, 1972 PULSE MOTOR ASSEMBLY[56] References Cited [72] Inventor: Tokuzo Inarlba, Tokyo, Japan UNITEDSTATES PATENTS Assignee: Kabushiki Keisha T e! y: Denki 3,348,08310/1967 lnariba ..3l0/l64 f f y l w l 3,549,918 12/1970 Croymans et al..310/112 x N1sh1kasuga1-gun, Arch: Prefecture, Japan PrimaryExaminer--D. F. Duggan [22] Filed: April 6, 1971 Attomey-Woodhams,Blanchard and Flynn 21 A 1. No.: 131 760 I 1 pp 57 ABSTRACT 30 Foreign Ali ti priority Data A pulse motor assembly comprising a plurality ofsynchronous motors connected 1n tandem. Each of the Apnl 1970 Japan a"A's/29214 synchronous motors includes a rotor having pole teeth eachtapering towards its free end which is formed as..3l0/;ti9623;(1g/7l/(l) a sharp pointed end The north and South polesof [58] Field 162464 manent magnet stator included in the respective310/111,: synchronous motors are staggered from each other by a distanceequivalent to one pole pitch divided by the number of the synchronousmotors connected.

5 Claims, 11 Drawing Figures if a ,1

3 25a 25o 22c 31 K 29 k 35 331 26 q 27 27 5 )y 32q' 32c 32 PATENTEDSEPIBI912 3.693.034

SHEEI 2 OF 4 INVENTOR 04 450 MOW/54 Mama/7% ATTORNEYS PATENTED 19 I9723,693, 034

sum 3 OF 4 INVENTOR ATTORNEYS 1 PULSE MOTOR ASSEMBLY This inventionrelates to a pulse motor assembly comprising two or more synchronousmotors connected in tandem and stepped by a predetermined angle at atime by reversing pulses of opposite polarities.

Unlike an induction motor, a pulse motor does not continuously rotate ata constant speed but it repeats start, acceleration, and halt everyinput pulse. Therefore, an output torque and moment of inertia should becarefully taken account of. Since a rotor of a conventional motor ismade of a permanent magnet which presents a high load moment, hunting (aphenomena wherein the number of input pulses is not proportional to thenumber of steps of an output shaft) is possibly observed or startcharacteristic is deteriorated when such a rotor is employed in a pulsemotor. Further, such a conventional motor has disadvantages that it getsso hot that a fan is required for cooling. Accordingly, the design andmanufacturing process of the motor are much complicated, resulting inlow efficiency of the motor for power dissipation.

It is, therefore, an object of the present invention to eliminate theabove-mentioned disadvantages and to provide an improved pulse motorassembly capable of minimizing an inertia of rotor and improving a stepresponse enough to prevent a possible hunting and a start failure.

It is another object of the present invention to provide a pulse motorassembly which is capable of employing a semiconductor circuit becauseof its minimized temperature rise as compared to the pulse motorassembly of the prior art, and which is capable of providing a highefficiency for low power dissipation.

It is a further object of the present invention to provide a pulse motorassembly in which a rotor has pole teeth tapered from their baseportions towards their free ends to form sharp-pointed ends so thatmagnetic resistance is gradually increased towards their free ends,whereby alternating magnetic fluxes can be distributed desirably toincrease output torque and efficiency to provide large rotating power bya small input.

Other objects of this invention will be obvious from the contents of thespecification hereinafter disclosed.

Essentially according to the present invention, there is provided apulse motor assembly comprising a casing; a partition provided in saidcasing to form rooms in cooperation with the casing; a rotary shaft madeof non-magnetic material and rotatably supported by said casing, and aplurality of synchronous motors mounted in the respective rooms formedby said partition and each including a multiphase exciting coil, apermanent magnet stator disposed concentrically with said exciting coiland magnetized to provide north and south poles alternating on theperiphery thereof, and a rotor fixed to said rotary shaft and having aplurality of pole teeth each tapered from its base portion towards itsfree end and disposed between said exciting coil and said permanentmagnet stator, said north and south poles of the permanent magnetstators included in the respective synchronous motors being staggeredfrom each other by a distance equivalent to one pole pitch divided bythe number of the synchronous motors mounted.

The invention will be better understood from the fol lowing descriptiontaken in connection with the accompanying drawings in which:

FIG. 1 is a longitudinal cross sectional view of a synchronous motorused in a pulse motor assembly according to the present invention;

FIG. 2 is a cross sectional view taken along line 11-" of FIG. 1;

FIG. 3 is a perspective view of a rotor;

FIGS. 4(a and (b) are explanatory sectional view showing thedistribution of magnetic flux about pole teeth of the rotor and apermanent magnet;

FIG. 5 is a longitudinal cross sectional view illustrating a preferredembodiment of a pulse motor assembly according to the present invention;

FIG. 6 is a circuit diagram of an exciting coil; and

FIGS. 7(a) through (e) are explanatory development view showing theoperational principle of the pulse motor assembly as shown in FIG. 5.

Referring now to FIGS. 1 through 4 which illustrate a synchronous motorused in a pulse motor of this invention, numeral 1 designates a casingof soft magnetic material which serves as a yoke of alternating magneticcircuit and has a base portion 2. F ixedly secured to said casing is anexciting coil 3 having a terminal 4 which, in turn, is to be connectedto an A.C. power supply. Secured at the center of the base portion 2 isa magnet receptacle 5 of soft magnetic material having an annularprojection 5a. An oil-impregnated bearing 6 is secured to said magnetreceptacle 5. Rotatably supported by said bearing 6 is a rotary shaft 7of non-magnetic material, to which fixedly secured at its upper endthrough a boss 9 is a rotor 8 having a plurality of pole teeth 8a eachtapered in its width from its base portion toward 'its free end. lnsidesaid annular projection 5a of the magnet receptacle 5 there is mounted acylindrical permanent magnet stator 10 of ferrite magnetic materialmagnetized to provide north and south poles alternating on the peripherythereof. The number of poles of the magnet stator 10 is even multiple ofthe number of pole teeth 8a of the rotor 8. The magnet stator 10 isfirmly held by a magnet holder 11 fixed to the bearing 6.

In operation, when an A.C. voltage is applied to the exciting coilthrough the terminal 4, an alternating magnetic field is produced in thecasing l and the pole teeth of the rotor 8 are all magnetizedalternately in north and south poles in synchronism with the frequencyof the power supply, causing attracting or repelling force between saidpoles teeth 8a of the rotor 8 and the poles of the magnet stator 10,whereby the rotor is rotated in synchronism with the frequency of saidA.C. power supply. Since the annular projection 5a formed on the magnetreceptacle 5 of soft magnetic material is arranged so as to face saidpole teeth 8a of the rotor 8 and abut on the magnet stator 10, themagnetic fluxes of the alternating magnetic field generated by theexciting coil are effectively interlinked with a magnetic fluxesproduced by said magnet stator 10.

The magnetic flux density in the pole teeth 8a of the rotor 8 is highestat their tip ends and the magnetic resistance thereof is largest also attheir tip ends because magnetic fluxes are, as shown in FIGS. 4(a and(b), leaked from the base portions of said pole teeth 8a owing to theirtriangular shape. Said magnetic fluxes are distributed over thesubstantial lengths of the-pole teeth 8a to be effectively interlinkedwith the magnetic flux generated by the magnet stator 10, applying largeattracting or repelling forces to the pole teeth 8a and resultantlyapplying a sufficient torque to the rotor 8. Thus, the efficiency of themotor is remarkably improved and a possible temperature rise is by farreduced.

Referring now to FIGS. to 7, there is illustrated a pulse motor assemblyaccording to the present invention which comprises two or moresynchronous motors connected in tandem as shown in FIG. 5. Statedillustratively, a partition 22 in the form of a soft magnetic materialplate is provided in a casing 21 at its intermediate portion to form tworooms in cooperation with said casing, in each of which a synchronousmotor of the type described above is mounted. Exciting coils 23, 23' aresecured to said casing 21 through locking rings 24, 24. Each of thecoils 23, 23' has a bobin on which two or more windings are wound. Theexciting coil employed in the illustrated embodiment is a two phase coilhaving two windings.

A magnet receptacle 25 is attached to the inner surface of the back ofthe casing 21 and a similar magnet receptacle 25' is attached to thecasing 21 around its opening. Secured to inner peripheries of annularprojections 25a, 25a formed on the magnet receptacle 25, 25', throughmagnet holders 26, 26', are magnet stators 27, 27, which are staggeredfrom each other by one half of the pitch of the pole width, as shown inFIG. 7.

A bearing holder 28 is fixed on the back side of the casing 21 andanother bearing holder 28' is fixed to the magnet receptacle 25'. Fittedto said bearing holders 28, 28' are oil-impregnated bearings 29, 29' bywhich a rotary shaft 30 of non-magnetic material is rotatably supported.Mounted on the opposite ends of the rotary shaft 30 are shaft supports31, 31' which minimize a lateral movement of the shaft 30. Secured tothe rotary shaft 30 through bosses 33, 33' are rotors 32, 32' havingpole teeth 32a, 320' each tapered from its .base portion towards itsfree end which is formed as sharppointed end. Numeral 34 designates aterminal for the exciting coils 23, 23', and numeral 35 designates apinion gear secured to the rotary shaft 30.

Referring particularly now to FIG. 6, a circuit diagram of the excitingcoils 23, 23 which have bobbins on which two windings 23a, 23b and 23a,23b are wound, respectively. One end of each of the-windings 23a, 23b isconnected to fixed contacts a, b of a switch SW,, respectively, whilethe other end of each of said windings is interconnected with eachother. Similarly, one end of each of the windings 23a, 23b is connectedto fixed contacts 0, d of a switch SW respectively, while the other endof each of said windings is interconnected with each other. Movablecontacts 2, f of the switches SW, and SW are connected to a positiveterminal of a power supply E while the junctions of the windings 23a and23b and the windings 23a and 23b are connected to a negative terminal ofsaid power supply E. By the actuation of the switches SW,, SW pulsesignals are applied to the windings 23a, 23b, 23a and 23b. Although amechanical switching means is shown in the illustrated embodiment of thepresent invention to generate pulse signals, a suitable electric circuitsuch as a flip-flop circuit may, of course, be alternatively employed togenerate such pulse signals through an electrical switching operation.

Operation of the above circuit is now described. When the movablecontacts e, f of said switches SW, and SW are in the neutral positions,or, when said exciting coils 23, 23 are deenergized, said rotor 32, 32'are kept in the respective positions shown in FIG. 7(a). Statedillustratively, the pole teeth 32a of the rotor 32 are positioned at onequarter of a pole pitch apart from pole interfaces of the magnet stator27 and the pole teeth 32a of the rotor 32 are also positioned at aquarter of a pole pitch apart from pole interfaces of the magnet stator27, or vice versa.

When the movable contact e of the switch SW, is connected to the fixedcontact a and the movable contact f of the switch SW to the fixedcontact c, pulse signals are applied to the windings 23a, 23a of theexciting coils 23, 23' so that the rotors 32, 32 are excited to providea north polarity. Thus, the pole teeth 320 are moved to the right inFIG. 7 due to the attracting force caused between said pole teeth 32aand the south poles of the magnet stator 27. Simultaneously, the poleteeth 32a are moved to the right due to the repelling force between saidpole teeth 32a and the north poles of the magnet stator 27'. Said poleteeth 32a and said pole teeth 32a are moved until they come to therespective positions shown in FIG. 7(b) in whichthe pole teeth 32a areat a quarter of a pole pitch apart from the respective next north polesof the magnet stator 27 and the pole teeth 32a are at a quarter of apole pitch apart from the respective previous north poles of the magnetstator 27'. In this connection, it is to be noted that the pole teeth32a, 32a are each tapered towards its end to be formed as asharp-pointed end, so that the flux density in each of the pole teethincreases towards its free end, providing a large rotation torque forthe rotors.

When the movable contacte of the switch SW, is connected to the fixedcontact b and a pulse signal is applied to the winding 23b of theexciting coil 23, the

rotor 32 is excited to provide south polarity and the pole teeth 32a aremoved to the right due to the repelling force caused between said southpoles of the pole teeth 32a and the south poles of the magnet stator 27.Incidentally, the pole teeth 32a of the rotor 32' are attracted to theright, since said south poles of the magnet stator 27 have largermagnetic force at their inter mediate portions, until said pole teeth32a of the rotor 32' are positioned as shown in FIG. 7(c) balancing withthe relation between the rotor 32 and the magnet stator 27.

Similarly, when the movable contact f of the switch SW is connected tothe fixed contact d, the winding 23b of the exciting coil 23' is excitedto magnetize the rotor 32 in south polarity. Thus, the rotors 32, 32 aremoved to the respective positions as shown in FIG. 7(d). When themovable contact e of the switch SW, is connected to the fixed contact a,the winding 23a of the exciting coil 23 is energized to magnetize therotor 32 in north polarity, Thus, the rotors 32, 32' are moved to theirrespective positions as shown in FIG. 7(e). By further switching theswitches SW,, SW, in similar way, the rotors 32, 32' are continuouslyrotated. Upon actuation of the exciting coils 23, 23' in a manner asdescribed above, the rotors 32, 32' are selectively magnetized in northor south polarities, and rotated due to the rotation of the rotors 32,32' may be reversed by operating, the switches in a reversed sequence.Although mechanical switching means are employed in thepresentembodiment, an electric circuit such as a flip-flop circuit mayalternatively be used to effect high speed electrical switchingoperation. Two synchronous motors connected in tandem are employed inthe present embodiment, the number of the synchronous motors is notlimited to this specified number. in any case, the poles of the magnetstators 27, 27' should be staggered from each other by a distanceequivalent to one pole pitch divided by the number of the synchronousmotors employed. Furthermore, though the exciting coils 23, 23' arearranged outside of the stator magnets 27, 27' in the presentembodiment, the stator magnets 27, 27' may be disposed outside of theexciting coils 23, 23' to accomplish the purpose. 7

As apparent from the foregoing descriptions, according to a pulse motorassembly of the present invention, which comprises a plurality ofsynchronous motors connected in tandem each having a rotor of softmagnetic material mounted between a multiphase exciting coil having aplurality of windings and a magnet stator magnetized to provide northand south poles alternating on its periphery, said rotor beingmagnetized alternately in north and south poles in synchronism with apulse signal applied to said exciting coil to cause an attracting orrepelling force between said rotor and the magnet stator for rotatingsaid rotor, the mass of the rotor may be by far reduced as compared witha permanent magnet motor of a conventional pulse motor made offerromagnetic material such as ferrite to provide an excellent pulserotor of small inertia and quick response to a pulse signal which isapplicable to a power source for digital-controlled output device or aservo-mechanism for machine tools or general industrial machine. Furtheraccording to the present invention, the pole teeth of the rotor aretapered towards their free ends which are formed as sharp-pointed endsso that alternating magnetic fluxes are distributed over their entirelengths to effectively interlink with magnetic fluxes produced by themagnet stator to provide large attracting and repelling forces for thepole teeth, thus applying a large rotating torque to the rotor andenhancing the efficiency of the motor. On the other hand, a possibletemperature rise in the motor is effectively prevented to eliminate anecessity of employing a cooling fan and enable the motor to be mountedwith a semiconductor circuit assembly.

it is intended that all matter contained in the foregoing descriptionand in the drawings shall be interpreted as illustrative only not aslimitative of the invention.

What is claimed is:

l. A pulse motor assembly comprising:

a casing;

a partition of soft magnetic material provided in said casing to formmagnetically shielded rooms in cooperation with the casing;

a rotary shaft made of non-magnetic material and r tatabl s ortedb saidcasin ,and plurality o s jmchron c ius motors mounted in the respectiverooms formed by said partition and each including a multiphase excitingcoil, a permanent magnet stator disposed concentrically with saidexciting coil and magnetized to provide north and south polesalternating on the periphery thereof, and a rotor fixed to said rotaryshaft and having a plurality of pole teeth each tapered from its baseportion towards its free end and disposed between said exciting coil andsaid permanent magnet stator,

said north and south poles of the permanent magnet stators included inthe respective synchronous motors being staggered from each other by adistance equivalent to one pole pitch divided by the number of thesynchronous motors mounted.

2. The device of claim 1 in which said casing includes an axiallyextending peripheral wall of soft magnetic material and a pair of endwalls, said plurality of synchronous motors being axially spaced alongand within said casing with one in each said room, said partitioncomprising a single soft magnetic material plate extending in radiallyoverlapping relation with the rotors of two adjacent motors, said rotorsof said adjacent motors being separated by said plate, said plateextending radially into contact with said casing peripheral wall, eachsaid adjacent motor having an alternately magnetic circuit including thesame plate.

3 The device of claim 2 including a pair of coaxial locking ringsextending fixedly and coaxially from opposite sides of said plate intoadjacent rooms, said rotor teeth in said adjacent rooms being spacedradially between said locking rings and said permanent magnet stator.

4. The device of claim 3 in which the two motors in the two roomsseparated by said plate are arranged in mirror imaged, back to backrelation, said plate being located in axially centered but spacedopposed relation to the permanent magnet stators of said two motors andseparated therefrom by radial portions of the two rotors of said twomotors, the pole teeth of said two rotors extending away from saidplate.

5. The device of claim 2 in which two coils are provided for each statorand set of pole teeth and including switch means for actuating said twocoils alternatively so that one is energized while the other isdeenergized, all pole teeth of agiven synchronous motor being energizedby said multiphase exciting coil with the same magnetic polarity.

1. A pulse motor assembly comprising: a casing; a partition of softmagnetic material provided in said casing to form magnetically shieldedrooms in cooperation with the casing; a rotary shaft made ofnon-magnetic material and rotatably supported by said casing, and aplurality of synchronous motors mounted in the respective rooms formedby said partition and each including a multiphase exciting coil, apermanent magnet stator disposed concentrically with said exciting coiland magnetized to provide north and south poles alternating on theperiphery thereof, and a rotor fixed to said rotary shaft and having aplurality of pole teeth each tapered from its base portion towards itsfree end and disposed between said exciting coil and said permanentmagnet stator, said north and south poles of the permanent magnetstators included in the respective synchronous motors being staggeredfrom each other by a distance equivalent to one pole pitch divided bythe number of the synchronous motors mounted.
 2. The device of claim 1in which said casing includes an axially extending peripheral wall ofsoft magnetic material and a pair of end walls, said plurality ofsynchronous motors being axially spaced along and within said casingwith one in each said room, said partition comprising a single softmagnetic material plate extending in radially overlapping relation withthe rotors of two adjacent motors, said rotors of said adjacent motorsbeing separated by said plate, said plate extending radially intocontact with said casing peripheral wall, each said adjacent motorhaving an alternately magnetic circuit including the same plate.
 3. Thedevice of claim 2 including a pair of coaxial locking rings extendingfixedly and coaxially from opposite sides of said plate into adjacentrooms, said rotor teeth in said adjacent rooms being spaced radiallybetween said locking rings and said permanent magnet stator.
 4. Thedevice of claim 3 in which the two motors in the two rooms separated bysaid plate are arranged in mirror imaged, back to back relation, saidplate being located in axially centered but spaced opposed relation tothe permanent magnet stators of said two motors and separated therefromby radial portions of the two rotors of said two motors, the pole teethof said two rotors extending away from said plate.
 5. The device ofclaim 2 in which two coils are provided for each stator and set of poleteeth and including switch means for actuating said two coilsalternatively so that one is energized while the other is deenergized,all pole teeth of a given synchronous motor being energized by saidmultiphase exciting coil with the same magnetic polarity.